1. Field of the Invention
The present invention relates generally to a Hybrid Electric Vehicle (HEV), and specifically to an HEV system controller that determines xe2x80x9cengine onxe2x80x9d status using peak engine cylinder pressure.
2. Discussion of the Prior Art
The need to reduce fossil fuel consumption and emissions in automobiles and other vehicles powered by an Internal Combustion Engine (ICE) is well known. Vehicles powered by electric motors attempt to address these needs. However, electric vehicles have limited range and limited power capabilities and need substantial time to recharge their batteries. An alternative solution is to combine both an ICE and electric traction motor into one vehicle. Such vehicles are typically called Hybrid Electric Vehicles (HEVs). See generally, U.S. Pat. No. 5,343,970 (Severinsky).
The HEV is described in a variety of configurations. Many HEV patents disclose systems in which an operator is required to select between electric and internal combustion operation. In other configurations, the electric motor drives one set of wheels and the ICE drives a different set.
Other, more useful, configurations have developed. For example, a Series Hybrid Electric Vehicle (SHEV) configuration is a vehicle with an engine (most typically an ICE) connected to an electric motor called a generator. The generator, in turn, provides electricity to a battery and another motor, called a traction motor. In the SHEV, the traction motor is the sole source of wheel torque. There is no mechanical connection between the engine and the drive wheels. A parallel Hybrid Electrical Vehicle (PHEV) configuration has an engine (most typically an ICE) and an electric motor that together provide the necessary wheel torque to drive the vehicle. Additionally, in the PHEV configuration, the motor can be used as a generator to charge the battery from the power produced by the ICE.
A parallel/Series Hybrid Electric Vehicle (PSHEV) has characteristics of both PHEV and SHEV configurations and is typically known as a xe2x80x9cpowersplitxe2x80x9d configuration. In the PSHEV, the ICE is mechanically coupled to two electric motors in a planetary gearset transaxle. A first electric motor, the generator, is connected to a sun gear. The ICE is connected to a carrier. A second electric motor, a traction motor, is connected to a ring (output) gear via additional gearing in a transaxle. Engine torque powers the generator to charge the battery. The generator can also contribute to the necessary wheel (output shaft) torque. The traction motor is used to contribute wheel torque and to recover braking energy to charge the battery if a regenerative braking system is used.
The desirability of combining an ICE with an electric motor is clear. The ICE""s fuel consumption and emissions are reduced with no appreciable loss of vehicle performance or range. Nevertheless, there remains a substantial opportunity to develop ways to optimize HEV operation.
On such area of development is determining if the engine is on. In a conventional vehicle, xe2x80x9cengine onxe2x80x9d status can be easily determined after xe2x80x9ckey onxe2x80x9d by comparing the actual engine speed to a threshold value that indicates the engine is producing torque and combustion. It can also be determined by simply listening for engine noise or feeling engine vibration. However, in an HEV the engine may not be running after xe2x80x9ckey onxe2x80x9d and sometimes not even when the vehicle is in motion. Therefore, it becomes necessary for the Vehicle System Controller (VSC) to identify xe2x80x9cengine onxe2x80x9d status before making powertrain torque determinations.
The prior art has disclosed systems to determine whether the engine is on. Unfortunately, these systems often relate specifically to conventional ICE vehicles. For example, in U.S. Pat. No. 5,372,101 to Hishiba, et al., engine speed is measured to determine if the engine is starting or running. This method would not work with an HEV because the HEV""s generator can spin the engine without combustion occurring. Therefore, engine speed in this situation would not be a reliable measurement of xe2x80x9cengine onxe2x80x9d status in an HEV.
In U.S. Pat. No. 5,601,058 to Dyches, et al., a method of measuring starter motor current is disclosed and in U.S. Pat. No. 6,009,369 to Boisurart, et al., a method of measuring alternator voltage is disclosed to determine if the engine is running. These two methods are also inapplicable to the HEV because the HEV does not use a conventional starter motor or alternator.
A possible solution to determine xe2x80x9cengine onxe2x80x9d status in an HEV is to use peak engine cylinder pressure measurement that is known in the prior art. Ion current/breakdown voltage correlates to the density of gas in the combustion chamber and in-cylinder pressures. The density of the gas is controlled by the throttle plate position, which is already known by the powertrain controller through other sensors. Therefore, peak in-cylinder pressure is a function of temperature only (assuming density is roughly known), and the temperature spikes dramatically when combustion takes place. When the powertrain controller for all cylinders infers this spike in temperature and pressure, it can be assumed that the engine is xe2x80x9crunningxe2x80x9d under its own power.
Several articles discuss this general correlation. See A. A. Martychenko, et al., A Study on the Possibility of Estimation of In-Cylinder Pressure by Means of Measurement of Spark Gap Breakdown Voltage, SAE 1999-01-1115 (1999); J. Forster, et al., Ion Current Sensing For Spark Ignition Engines, SAE 1999-01-0204 (1999); S. Yuichi, et al., Spark Plug Voltage Analysis for Monitoring Combustion in an Internal Combustion Engine, Journal of the Society of Automotive Engineers of Japan V 47, pp. 32 (1993).
Martychenko describes how to estimate peak cylinder pressure using secondary ignition voltage. Circuits monitoring spark plug gap breakdown voltage for each engine cylinder are fed into a powertrain control module (PCM). The PCM compares the breakdown voltage observed with a predetermined value to represent the occurrence of stable combustion. At that point, the PCM will set a software flag indicating that the engine has indeed xe2x80x9cstarted.xe2x80x9d Martychenko also mentions a similar method of determining in-cylinder pressure based on ion current across the spark plug gap.
Although ion current/breakdown voltage is known, these articles do not incorporate the correlation process into a logic scheme of a Vehicle System Controller to determine if the engine is on and combustion is occurring in an HEV.
Accordingly, the present invention provides a method and system for determining xe2x80x9cengine onxe2x80x9d status in an HEV.
The HEV relies upon the generator motor to spin up or xe2x80x9cmotorxe2x80x9d the engine. Therefore, it is not possible to measure engine speed to determine whether the engine is running. It is an object of the present invention to provide a method and apparatus to determine xe2x80x9cengine onxe2x80x9d status in an HEV by measuring peak engine cylinder pressure using ion current/breakdown voltage in the HEV engine. If the ion current/breakdown voltage meets a certain threshold, the Vehicle System Controller will conclude combustion is occurring and the engine is running.
The present invention provides a reliable method to determine xe2x80x9cengine onxe2x80x9d status by measuring the ion current/breakdown voltage across a spark plug within the engine. The ion current/breakdown voltage is then compared to a calibratable threshold. If the ion current/breakdown voltage exceeds the calibratable threshold then combustion is occurring within the engine and the engine is running. Once the VSC determines the engine is on, it can make engine torque requests.
A system to perform the above method comprises a controller, a generator, an engine, and measuring device to determine the ion current/breakdown voltage. The controller determines the need for the engine to be on, starts the engine, and then determines xe2x80x9cengine onxe2x80x9d status by comprising the ion current/breakdown voltage to a calibratable threshold.